The present invention is related to the field of heat exchangers, especially the heat exchangers that are used in aircraft to control the temperature of the bleed air from the aircraft engine.
Aircraft comprise several systems which are intended to deal with air flows throughout the aircraft. Air is needed to feed some parts of the aircraft, such as air conditioning, and must therefore meet particular values of pressure and temperature.
Aircraft comprised in the state of the art deal with these requirements by providing heat exchanging packs, which usually comprise a pair of heat exchangers, a primary heat exchanger and a secondary heat exchanger, as seen, for example, in document U.S. Pat. No. 6,427,471 A1.
Hot, high pressure bleed air from an engine, an auxiliary power unit, or a ground source, is directed into the hot side of the primary heat exchanger. In turn, cold air (at ambient pressure and temperature) enters in the cold side of the secondary heat exchanger. Hot air is cooled and then enters a compressor. After that, it enters the hot side of the secondary heat exchanger, where it is cooled by the cold air that enters the cold side of said secondary heat exchanger. After that, it expands and cools in the turbine, which also moves the former compressor, and goes to the air conditioning facilities. Cold air that enters the cold side of the secondary heat exchanger, after cooling the air in the hot side of the secondary heat exchanger, enters the cold side of the primary heat exchanger and cools the hot side in the secondary heat exchanger. After that, heated cold air is exhausted to ambient. All these steps may be seen in the aforementioned document.
These heat exchanging packs are suitable for providing the air from the engine with the suitable properties that make it adequate for its use in the cabin or in other aircraft facilities. However more than 100 kW of energy is typically thrown away to atmosphere through the RAM air channel because of the air cooling in the primary heat exchanger. This efficiency is improved by this invention.